Simulation of induced acoustic emission in fractured porous media

Abstract

Acoustic/microseismic Emissions (AE) in naturally fractured porous media are the result of local instability along internal interfaces and the sudden release of strain energy stored in the rock matrix. This rapid release of energy, stimulates high-frequency components of the dynamic response of the rock mass, inducing mechanical wave propagation. In this article an enriched finite element model is employed to concurrently simulate the interface instability and the induced wave propagation processes in a fractured porous media.Harmonic enrichment functions are used in the context of the Generalized Finite Element Method (GFEM) to suppress the spurious oscillations that can appear in wave propagation/dynamic modelings using regular finite elements. To model the fractures, the Phantom Node Method (PNM) is employed with the GFEM.The frictional contact condition at material interfaces is modeled using a stable augmented Lagrange multiplier approach. Through various parametric studies it's shown that i) decreasing the permeability leads to an increase in the frequency and a decrease in the amplitude of the acoustic signal; ii) increasing viscous damping leads to narrower frequency spectrum and decreased magnitude of the emitted acoustic signal;iii) increasing damping leads to a transition from transient wave propagation to diffusion-dominated AE response; iv) increasing interface friction leads to more pronounced stick-slip behavior and higher amplitude AE-without interface friction there is no AE. Lastly, the numerical illustrations demonstrate the superior capability of the enriched model (in comparison with regular finite element models) in suppressing the spurious oscillations in AE solutions.

An enriched mixed finite element model for the simulation of microseismic and acoustic emissions in fractured porous media with multi‐phase flow and thermal coupling

“…Original real nodes and additional phantom nodes are depicted by solid and hollow circles, respectively. The shaded portion of each superimposed element represents the active part of those elements 26 …”

“…In such methodologies, mechanical wave aspects like propagation and interactions with discontinuities, signal attenuation, reflection and coalescence may not be included. As an attempt in trying to partially address the existing shortcomings and gaps in the literature of induced AE and ME simulation, Komijani and his coworkers recently introduced enriched finite element methods 24,25 and numerical modelling approaches developed and tailored for simulation of the coupled process of localization-induced wave emissions in porous media with single-phase fluid flow in the cases of ME induced by shear-slip instability at pre-existing fractures 26 and tensile fracture propagation induced AE. 27 This article presents a novel enriched mixed finite element formulation for fully coupled dynamic thermo-hydromechanical (THM) simulation of deformable fractured porous media with three-phase (water-gas-nonaqueous) fluid flow and thermal coupling.…”

A mixed nonlocal finite element model for thermo‐poro‐elasto‐plastic simulation of porous media with multiphase fluid flow

“…Komijani and his co-workers also extended the use of the developed enriched finite element models to simulation of induced microseismic and acoustic emissions due to fracture reactivation and tensile fracture propagation in single phase and multi-phase flow cases. [12][13][14] Numerical modellings of the coupling between solid deformation, fluid flow, and heat transfer with or without material nonlinearity considerations dates back to the works of Lewis and Schrefler 15 (1-phase and 2-phase flow, isothermal and non-isothermal, elasto-plastic), Lewis et al 16 and Rahman and Lewis 17 (3-phase flow, isothermal, elastic). The topic was later extended and investigated by Ngien et al 18 and Gajo et al 19 (3-phase flow, isothermal, elastic), Ghorbani et al 20 (2-phase flow, isothermal, elasto-plastic), Gong et al 21 (3-phase fluid (passive gas phase), non-isothermal, elasto-plastic).…”

Acoustic Emission Signal Fault Diagnosis Based on Compressed Sensing for RV Reducer

“…For weak fault signals, the characteristics of fault signals are very weak and easily immersed in the noise of other components, so they cannot be effectively diagnosed [ 5 ]. AE refers to the phenomenon that materials are deformed or fractured by external or internal forces, releasing stress-strain in the form of elastic waves [ 6 ]. AE technology can be used for non-destructive testing of materials or structures with damage or initial damage.…”